From German Patent Application No. DE 198 49 210, for example, a fuel injector is known which has a nozzle body that has a tubular design at its downstream side, and at whose downstream end a sealing seat and a discharge orifice are located. The tubular section of the nozzle body can be inserted into a receiving bore of a cylinder head. The nozzle body is sealed from the receiving bore of the cylinder head, which has a diameter that corresponds to the radial extension of the nozzle body, by a seal having approximately the geometry of a hollow cylinder.
For fixing the seal in position on the nozzle body, the nozzle body is provided with a circumferential groove into which the seal is inserted, the groove being introduced, for example, by desurfacing the nozzle body. To be used as materials are elastic materials which, for installation in the groove, can be slipped over the nozzle body.
Moreover, from German Patent Application No. DE 198 08 068, as well, a fuel injector is known in which a sealing element is positioned on the nozzle body. The seal is made of a metallic material and expands in the radial direction under the influence of the temperature generated by the combustion process. This may be achieved either by a shape-memory alloy or by the use of a bi-metal seal. As in German Patent Application No. DE 198 49 210, a groove in the nozzle body may be used for the fixation.
During operation of the internal combustion engine, the metal sealing ring heats up and expands, thereby increasing the sealing effect during operation. To facilitate the installation, the metal seal has a slightly smaller diameter than the receiving bore introduced in the cylinder head for the fuel injector.
A primary disadvantage of the sealing approach proposed in German Patent Application No. DE 198 49 210 is the high temperature to which the seal is exposed. Especially in directly injecting internal combustion engines a high-speed resistance of non-metallic sealing materials cannot be ensured.
The fuel injector described in German Patent Application No. DE 198 08 068 has the disadvantage that the sealing effect of the metallic seal is temperature-dependent. Following a cold start of the internal combustion engine, some time elapses before the combustion process heats up the materials in the vicinity of the combustion chamber to such a degree that, due to heat conduction, the temperature leading to the required deformation is achieved in the seal. For this reason, another seal is required, in addition to the mentioned seal, in order to seal the combustion chamber from the external space at the start of operation of the internal combustion, in order not to lose any compression pressure.
Also disadvantageous are the costly materials that are used in the production of metal seals that deform as a function of temperature. A shape-memory alloy has a transition temperature that is adapted to the intended application. In order to reliably ensure this transition temperature, a narrow range is often required for the manufacturing process. This not only causes an increase in the development costs for the alloy but also raises the cost when used in series production.
The use of a bimetal seal requires the seal to be affixed on the nozzle body which serves as a counter bearing in the deformation. However, installing the bimetal in a groove, for instance, is difficult since the properties of the material change when one of the two metals undergoes non-elastic deformation during installation.